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Working principle

How does the Contextual Instruments Capacitance Meter measure capacitance ?

Core Measurement Method

Capacitance measurement is based on the principle of "discharge time measurement" of an RC network. This process occurs in three distinct phases:

  • 1. Pre-charge phase: The capacitor is charged through a series resistor to a level close to the supply voltage. This approach reduces mechanical stress on the capacitive sensor, (particularly important for MEMS applications).
  • 2. Full-charge phase: The capacitor is then completely charged to VDD without any series resistor, ensuring a complete charge.
  • 3. Discharge phase: The capacitor is discharged through a calibrated discharge resistor to 0V. The discharge time is directly proportional to the capacitance according to the relationship: τ = k × R × C where τ is the discharge time, R is the discharge resistance, and C is the measured capacitance.

Ratiometric Approach

To eliminate systematic errors, the system uses a ratiometric approach, comparing the measured capacitor to a reference capacitor: τN/τref = CN/Cref This method eliminates most influences of temperature, voltage, and other environmental factors, as they affect both measurements identically.

Digital Signal Processing

After measurement, an integrated 32-bit DSP:

  • Calculates capacitance ratios
  • Applies compensation algorithms
  • Performs linearization via polynomial calculations
  • Compensates for temperature effects
  • Produces results with resolution reaching 20 bits